Respiration impedance measuring device and respiration impedance display method

Abstract

Continuous measurement of breathing impedance with extremely high precision is enabled by executing noise elimination. A loudspeaker applies an air vibration pressure by an oscillation wave to an oral cavity, the oscillation wave being obtained by frequency-cuffing so executed that the oscillation wave has only the frequency component that is left after the culling is executed from a plurality of different frequencies and being generated by a pulse signal for pulse drive with pulses made positive and negative separately in correspondence to the time of exhalation and the time of inhalation. A pressure inside the oral cavity is detected and a breathing flow is detected, and a signal obtained by the detection is Fourier-transformed to obtain a spectrum. Analysis of the spectrum is performed to obtain breathing impedance.

The invention claimed is: 
     
       1. A respiratory impedance measuring apparatus comprising:
 a pressurizing means for applying an air vibration pressure to inside of an oral cavity; 
 a pressure detecting means for detecting pressure signals inside of an oral cavity; 
 a flow detecting means for detecting flow signals generated by breathing; 
 a timing detecting means for detecting time points at which exhalation and inhalation switches, based on output signals from the flow detecting means; 
 a pulse signal generating means for generating pulse signals of a predetermined frequency, wherein the pulse signals are switched between positive and negative based on the time points; 
 a control means for controlling the pressurizing means by using the pulse signals generated by the pulse signal generating means, and generating the air vibration pressure by oscillation waves of the pulse signals, wherein the predetermined frequency of the pulse signals generated by the pulse signal generating means is greater than a frequency of the flow signals generated by breathing; 
 a Fourier transforming means for obtaining Fourier transform spectrums by Fourier transforming the pressure signals and the flow signals; 
 an extracting means for obtaining first spectrums that contain oscillation wave components and respiratory signal components from the Fourier transform spectrums of the pressure signals and the flow signals, extracting second spectrums that contain the respiratory signal components from the Fourier transform spectrums of the pressure signals and the flow signals, and obtaining the oscillation wave components by subtracting the second spectrums from the first spectrums; and 
 a computing means configured for obtaining respiratory impedance by dividing the oscillation wave components of the Fourier transform spectrums of the pressure signals with the oscillation wave components of the Fourier transform spectrums of the flow signals for each frequency of the Fourier transform spectrums of the pressure and flow signals. 
 
     
     
       2. The respiratory impedance measuring apparatus of  claim 1 , wherein
 the control means generates the air vibration pressure by the oscillation wave having only n/T 1  (n: an integer, T 1 : a real number) frequency components, by using pulse waves having a cycle of T 1 . 
 
     
     
       3. The respiratory impedance measuring apparatus of  claim 1  or  2 , wherein
 the control means includes a signal input means that supplies an input signal to the pressurizing means such that an oscillation wave having a desired pressure waveform is an output signal, based on reverse computation using an input signal and an output signal of the pressurizing means and a transfer function of the pressurizing means. 
 
     
     
       4. The respiratory impedance measuring apparatus of  claim 3 , wherein
 the signal input means supplies to the pressurizing means as an input signal a signal obtained by adding a specific value to each of frequency components of the signal obtained by the reverse computation, or by reverse computing a signal formed by adding an impulse to an onset portion of the output signal. 
 
     
     
       5. The respiratory impedance measuring apparatus of  claim 2 , wherein
 signal processing is carried out in a signal processing section T 2  (T 2 =mT 1  (m denotes an integer of 1 or larger)). 
 
     
     
       6. A respiratory impedance measuring method comprising:
 a pressurizing step of applying an air vibration pressure to an inside of an oral cavity by using a pressurizing means; 
 a flow detecting step for detecting flow signals generated by breathing by using a flow detecting means; 
 a pressure detecting step of detecting pressure signals inside of an oral cavity by using a pressure detecting means; 
 a timing detecting step of detecting time points at which exhalation and inhalation switches, based on output signals from the flow detecting step by using a timing detecting means; 
 a pulse signal generating step of generating pulse signals of a predetermined frequency, wherein the pulse signals are switched between positive and negative based on the time points by using a pulse signal generating means; 
 a controlling step, by using a control means, of controlling the pressurizing step by using the pulse signals generated by the pulse signal generating step, and generating the air vibration pressure by oscillation waves of the pulse signals, wherein the predetermined frequency of the pulse signals generated by the pulse signal generating step is greater than a frequency of the flow signals generated by breathing; 
 a Fourier transforming step of obtaining Fourier transform spectrums by Fourier transforming the pressure signals and the flow signals by using a Fourier transforming means; 
 an extraction step of obtaining first spectrums that contain oscillation wave components and respiratory signal components from the Fourier transform spectrums of the pressure signals and the flow signals, extracting second spectrums that contain the respiratory signal components from the Fourier transform spectrums of the pressure signals and the flow signals, and obtaining the oscillation wave components by subtracting the second spectrums from the first spectrums by using an extraction means; and 
 a computing step, by using a computing means, configured for obtaining respiratory impedance by dividing the oscillation wave components of the Fourier transform spectrums of the pressure signals with the oscillation wave components of the Fourier transform spectrums of the flow signals for each frequency of the Fourier transform spectrums of the pressure and flow signals. 
 
     
     
       7. The respiratory impedance measuring method of  claim 6 , wherein the control step generates the air vibration pressure by the oscillation wave having only n/T 1  (n: an integer, T 1 : a real number) frequency components by using pulse waves having a cycle of T 1 . 
     
     
       8. The respiratory impedance measuring method of  claim 6  or  7 , wherein the control step comprises a signal input step that supplies an input signal to the pressurizing step such that an oscillation wave having a desired pressure waveform is an output signal, based on reverse computation using an input signal and an output signal for the pressurizing step and a transfer function of the pressurizing step. 
     
     
       9. The respiratory impedance measuring method of  claim 8 , wherein the signal input step supplies to the pressurizing step as an input signal a signal obtained by adding a specific value to each of frequency components of the signal obtained by the reverse computation, or by reverse computing a signal formed by adding an impulse to an onset portion of the output signal. 
     
     
       10. The respiratory impedance measuring method of  claim 7 , wherein signal processing is carried out in a signal processing section T 2  (T 2 =mT 1  (m denotes an integer of 1 or larger)).